45Appendix A. Watchdog TimerThe Watchdog Timer is a device to ensure that standalonesystems can always recover from catastrophic conditions thatcause the CPU to crash. This condition may have occurred byexternal EMI or a software bug. When the CPU stops workingnormally, hardware on the board will perform hardware reset(cold boot) to bring the system back to a known state.Three I/O ports control the Watchdog Timer.443 Write Set Watchdog Time period443 (hex) Read Enable the refresh the WatchdogTimer043/843 (hex) Read Disable the Watchdog TimerPrior to enable the Watchdog Timer, user has to define Timerfirst. The output data is a value of time interval and the rangeof the value is from 01(hex) to FF (hex) and time interval 1 secto 255 sec.Data Time Interval01 1 sec02 2 sec03 3 sec04 4 sec......FF 255 sec
